The present invention relates to a process for the preparation of phenol from cumene.
As is known, phenol can be produced from cumene. The production process takes place in two phases. In the first phase, the cumene is oxidized to cumene hydroperoxide (CHP), with conversions which range from 20-35% by weight, in the second phase the CHP is acid cleaved into phenol and acetone with an acid, generally sulfuric acid. Between the first and second phase, there is generally a concentration step in which the CHP is concentrated to 70-90% by weight.
At the end of the acid cleaved reaction, which is extremely exothermic, the reaction mass is neutralized and the phenol is then recovered by distillation.
Since both the oxidation reaction and the subsequent acid cleaved reaction are accompanied by undesired secondary reactions, it is necessary to arrange methods/equipment, for carrying out the two operative stages described above, which can limit this drawback. In particular, by-products are produced through the secondary reactions as, for example, dicumyl peroxide (DCP) and dimethyl benzyl alcohol (DMBA) which, after downstream treatments, are selectively transformed into phenol and alpha-methylstyrene. The latter, after hydrogenation, forms cumene and can then be recycled.
Industrially, the oxidation reaction of cumene is effected by means of specific reactors, known as “air-lift” reactors, substantially consisting of a cylindrical structure inside which a second cylinder, open at the ends, is coaxially positioned, which allows the internal recirculation of the reaction mass. Said second cylinder is known by experts in the field, with the term “downcomer”. An example of an air-lift reactor is provided in FIG. 1A, which illustrates the essential elements of the reactor comprising the outer mantle, the downcomer and the feeding/discharge points of the reagents and reaction products in addition to the gas and vapours vents.
The reagents, cumene and a gas containing oxygen, preferably air, are fed to the base of the reactor in continuous and are recycled, again continuously, in the interior through the downcomer. A gas phase, consisting substantially of residual air and vapours, is discharged from the head of the reactor together with the reaction product, a mixture consisting essentially of CHP and non-reacted cumene, in addition to possible by-products.
After concentration in CHP, the reaction product can be temporarily stored and is then subjected to a cleavage reaction. On an industrial scale, this second reaction takes place in a closed cycle reactor known to experts in the field as “loop” reactor. In particular, this reactor, represented in FIG. 2, consists of tube A in which there is an inlet of the acid component (1) and an inlet, upstream of this, of CHP (2) and acetone (3). The acetone, which is one of the two products deriving from the cumene hydroperoxide cleavage, is introduced with the function of reaction moderator, in order to increase the overall yield of the process. The reaction mixture then rapidly passes in the tubes of a tube-bundle reactor (B), while the heat of reaction is removed with cooling water, fed and dischrged through (4) and (5), flowing on the shell side. The reaction mixture is re-fed to the tube (A) and the cycle continues. The phenol produced (together with the acetone) is discharged in continuous from (6).
The Applicant has now found a process for the production of phenol from cumene which is alternative to the process known in the state of the art. This new process, as far as the oxidation phase is concerned, improves selectivity to CHP and is simpler to manage as, for example, it allows a better control of the temperature in favour of the safety. As far as the cleavage reaction is concerned, the process has lower management costs, due to a smaller load to be processed by the recirculation pump, and higher selectivities to phenol and alpha-methylstyrene.